In recent years, in order to achieve device miniaturization, display devices having a touch panel function in which the display unit and the input unit are integrally formed are in wide use. In particular, in mobile terminals such as mobile phones, PDAs (personal digital assistants), and table PCs, display devices having touch panels that can detect a position of contact if a finger or an input stylus is brought into contact with the surface of the display unit are widely used.
As touch panels, conventionally, various types of touch panels such as the so-called resistive film type (pressure-sensing) and the capacitive type are known, and among those, the so-called capacitive type touch panels using the capacitive method in which a contact position is detected by changes in capacitance are widely used in display devices for mobile devices.
Such capacitive touch panels are installed outside of the display panel and are widely used.
In Patent Document 1, for example, a conventional capacitive touch panel such as that shown in FIG. 8 is disclosed.
As shown, a display device 100 including a conventional capacitive touch panel is configured as follows.
A liquid crystal display panel 111 includes a TFT substrate 114 and a color filter substrate 115, and between the two substrates 114 and 115, a liquid crystal layer (not shown) is sandwiched.
An upper polarizing plate 112 is provided on the top surface of the liquid crystal display panel 111, and a lower polarizing plate 113 is provided on the bottom surface of the liquid crystal display panel 111.
Also, on the bottom surface side of the liquid crystal display panel 111 (where the lower polarizing plate 113 is provided), a backlight 116 for radiating light to the liquid crystal display panel 111 is provided.
As shown, on one end of the TFT substrate 114, a driver circuit 103 and an FPC substrate 105 are provided.
On the other hand, the touch panel substrate 107 is bonded to the liquid crystal display panel 111 through a first adhesive 108, and on the surface of the touch panel substrate 107 facing the liquid crystal display panel 111, a transparent electrode layer 110 to be a shield layer that blocks noise originating from the liquid crystal display panel 111 is provided.
On the top surface of the touch panel substrate 107, a front surface protective plate 101 is bonded by a second adhesive 109.
A conductive member 106 for connecting the transparent electrode layer 110 to be the shield layer to ground potential is provided, and in addition, a spacer 102 is inserted between the touch panel substrate 107 and the TFT substrate 114.
Also, the FPC substrate 104 is connected to a touch panel control circuit (not shown), and sensor electrodes provided on the top surface of the touch panel substrate 107 and a control circuit (not shown) of the touch panel are electrically connected to each other through the FPC substrate 104. Also, an appropriate voltage such as ground potential is supplied through the FPC substrate 104 to the transparent electrode layer 110 provided on the bottom surface of the touch panel substrate 107. Thus, the FPC substrate 104 is connected to input terminals provided on the top surface of the touch panel substrate 107, and therefore, there is a need to provide wiring lines from the input terminals to the transparent electrode layer 110 provided on the bottom surface in order to electrically connect the input terminals to the transparent electrode layer 110.
FIG. 9 shows another example of a conventional capacitive touch panel disclosed in Patent Document 1.
As shown, on the bottom surface of the touch panel substrate 125, a shield layer 110 is formed, while on the top surface of the touch panel substrate 125, an X sensor layer 134 and a Y sensor layer 138 made of a transparent conductive layer are formed. On portions of the X sensor layer 134, a wiring layer 135 made of a silver alloy is formed, and on the top surface of the touch panel substrate 125, a first insulating layer 136, contact holes 137 formed in the first insulating layer 136, and a second insulating layer 139 are provided.
A connecting terminal 127 has a structure in which the wiring layer 135 made of the silver alloy, and the Y sensor layer 138 are layered on the X sensor layer 134.
Non-Patent Document 1 discloses the possibility of attaining a thin touch panel substrate 200 by forming a polyimide film on a glass substrate, then forming a sensor electrode layer, and peeling away the glass substrate, as shown in FIG. 10.
As shown in FIG. 10, the thin touch panel substrate 200 has a structure in which a buffer layer 202, electrode layers 203 made of a transparent conductive layer, an interlayer insulating layer 204, a conductive layer 205 for connecting two electrically separated electrode layers 203 through contact holes formed in the interlayer insulating layer 204, and an anti-reflective layer 206 are layered in that order on the polyimide substrate 201.
Also, Patent Document 2 discloses a display device including a touch panel such as that shown in FIG. 11.
As shown, the touch panel substrate 304 is made of PET at a thickness of 0.1 to 0.2 mm, and an X sensor pattern 303 is formed on the top surface of the touch panel substrate 304, and a Y sensor pattern 306 is formed on the bottom surface of the touch panel substrate 304.
On the bottom surface of another PET substrate 309, a shield layer 310 is formed, and a hard coat material 312 for protecting the shield layer 310 is provided.
A surface panel 301 is bonded from the top side of the touch panel substrate 304 through an optical adhesive 302, and the other PET substrate 309 is bonded from the bottom side of the touch panel substrate 304 through an optical adhesive 305.